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ISO1541: ISO1541 VOL of 0.6V Causing issues

Jacob Bolduc
Prodigy 30 points

Part Number: ISO1541
Other Parts Discussed in Thread: INA238, INA233

I Am using the ISO1541 to isoltate a high voltage output with an INA238 that is reading the voltage. I also have another ISO1541 for measuring another high voltage output in the same configuration example of one attached.

 

The issue is all applications show that the main I2C bus should be connected to SDA/SCL2 to be able to support the higher capacitance of the main bus as well as have VOL much closer to zero, however the VIL of the INA233 is 0.4V so the logic low of the ISO on the SDA/SCL1 side will not register as a zero to the INA233.

So i tried flipping the direction of the ISO so the 1 side was facing the main bus. However this causes issues when using multiple ISO because the logic low of one of them is seen as a high by the other.

I am at a loss of what to do beside adding another level shifter between the ISO and the INA. Is this truely the only option?  

 

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  • 0
    TI__Guru 57445 points

    Hi Jacob,

    Sorry to hear about the issues.

    Yes, bidirectional operation implementation in I2C isolators does require them to have non-standard logic thresholds at least on one side. This is a standard approach in the industry. Therefore, they might not necessarily be compatible with some devices. The best way to address this is to use an I2C buffer between ISO and INA.

    Please do also check if there are any other INA devices that might be compatible with ISO1541, thanks.


    Regards,
    Koteshwar Rao